A friction plate is used, in a transmission gear, for example, of an automobile, to allow a clutch-side and a gear-side to be rotated in a synchronous fashion, in order to prevent any shock upon gear shifting.
A conventional friction plate has been manufactured by a method comprising: punching a steel plate into an ring-like or annular body by means of a press machine, or coiling a web of steel plate so as to cause the broader surface to be extended in a common plane; cutting the superposed portions to form opposite ends; and then welding the opposite ends together.
It is noted, however, that a large amount of mills ends are produced during punching operation by means of a press machine, whereby loss of material is increased. Thus, the punching method is not advantageous in terms of manufacturing cost.
It is also noted that, according to the coiling method, it is necessary for weld overlays to be removed after welding, so as to obtain a plain surface. Thus, finishing works, such as grinding and/or buffing should be performed, whereby process step are complicated. When the opposite ends are not welded together so as to be remained "un-fixed", no finishing works are required. It is noted, however, that a friction plate is meshed with a gear incorporated in a transmission and rotated at higher speeds (at a maximum speed of about 8,000 rpm). Thus, the friction plate would be expanded in its outer diameter due to a centrifugal force, when the opposite ends of the friction plate are not connected together. This causes deficiency in that the friction plate will be in contact with a part around it.
A main object of the invention is to reduce or eliminate loss or waste of material and to reduce manufacturing cost.